Experimental and observational studies suggest that dietary fat influences the development of prostate cancer. Polyunsaturated fats appear to have a more adverse effect than saturated fats on tumor occurrence, and within the family of polyunsaturated fatty acids, omega-6 fatty acids appear to enhance risk while omega-3 fatty acids reduce risk. This proposal will evaluate whether or not specific or total levels of fatty acids measured in erythrocyte (red blood cell) membranes, a biomarker of recent fat intake, are associated with prostate cancer in middle aged men. The specific aims of the proposed investigation are to test the following hypotheses: 1) Levels of omega-3 fatty acids (eicosapentaenoic, docosahexaenoic, total omega-3) are higher in controls as compared to men with prostate cancer; and 2) Levels of omega-6 fatty acids (linoleic, arachidonic, total omega-6) are higher in men with prostate cancer as compared to controls. In collaboration with local physicians, we will identify 70 White and African-American men between the ages of 40 and 64 who reside in King County and who are newly diagnosed with prostate cancer between June I, 1995 and May 31, 1996. We plan to collect a blood sample prior to any treatment for prostate cancer. In addition, the men will be interviewed about 3 to 6 months later regarding social and demographic factors, family history of prostate cancer, dietary intake, and other risk factors for prostate cancer as part of a larger on-going population-based study. Blood samples will be obtained at the time of interview for 140 controls who will be identified through random digit dialing, frequency matched with cases according to five year age intervals, and who are interviewed and have blood drawn between June l, 1995 and May 31, 1996. The blood samples will be processed, and washed erythrocytes will be stored frozen until analysis. Gas-liquid chromatography will be used to determine the fatty acid profile of the red cell membranes, and will include measurement of 25 specific fatty acids. Descriptive, stratified, and multivariate analyses will be performed in order to examine differences in fatty acid levels between cases and controls. The proposed study could potentially help clarify the role of dietary fats in relation to prostate cancer. If omega-3 fatty acid levels are found to be negatively associated with prostate cancer, the findings could have substantial public health implications for cancer prevention.